The present invention relates to an energy storage system and more particularly to the use of carbon dioxide (CO2) in such energy storage system for direct storage and retrieval of energy.
At least some known power generation systems include a power-producing turbine system that uses CO2 as the working fluid. Such systems may include storage and release modes where they store potential electrical energy in gaseous CO2 and then release the energy from the gas through a change in temperature and/or pressure. At least some known power generation systems channel gaseous CO2 from a turbine to a storage tank that holds CO2 at its triple point to condense the gaseous CO2. However, condensing the gaseous CO2 into liquid CO2 within the storage tank at the triple point pressure yields only a portion of the energy contained in the system and is inefficient.